C语言经典练习例子教学

#include <stdio.h> #include <stdlib.h> #include <dos.h> #include <string.h> int check_for_ems(void) { union REGS inregs, outregs; struct SREGS segs; int major, minor; // DOS version struct DeviceHeader { struct DeviceHeader far *link; unsigned attributes; unsigned strategy_offset; unsigned interrupt_offset; char name_or_number_of_units[8]; } far *dev; int i; char driver_name[9]; // Get the DOS version inregs.x.ax = 0x3001; intdos (&inregs, &outregs); major = outregs.h.al; minor = outregs.h.ah; if (major < 2) return(0); // Requires DOS 2.0 else { // Get the list of lists inregs.h.ah = 0x52; intdosx (&inregs, &outregs, &segs); if (major == 2) dev = (struct DeviceHeader far *) MK_FP(segs.es + 1, outregs.x.bx + 7); else if ((major == 3) && (minor == 0)) dev = (struct DeviceHeader far *) MK_FP(segs.es + 2, outregs.x.bx + 8); else dev = (struct DeviceHeader far *) MK_FP(segs.es + 2, outregs.x.bx + 2); while (FP_OFF(dev) != 0xFFFF) { if (dev->attributes & 0x8000) { // Character device for (i = 0; i < 8; i++) driver_name[i] = dev->name_or_number_of_units[i]; driver_name[8] = NULL; } if (! strcmp(driver_name, "EMMXXXX0")) return(1); // Found driver dev = dev->link; } } return(0); } void main (void) { union REGS inregs, outregs; struct SREGS segs; unsigned handle; unsigned page; unsigned index, page_number; unsigned page_frame_address; char far *data; if (check_for_ems()) { inregs.h.ah = 0x40; int86 (0x67, &inregs, &outregs); // Make sure EMS is functional if (outregs.h.ah == 0) { // Allocate a handle for 5 pages inregs.h.ah = 0x43; inregs.x.bx = 5; int86 (0x67, &inregs, &outregs); if (outregs.h.ah == 0) { handle = outregs.x.dx; // Get the page frame address inregs.h.ah = 0x41; int86 (0x67, &inregs, &outregs); if (outregs.h.ah == 0) { page_frame_address = outregs.x.bx; // map the first 4 pages for (page_number = 0; page_number < 4; page_number++) { inregs.h.ah = 0x44; inregs.h.al = page_number; // Physical page inregs.x.bx = page_number; // Logical page inregs.x.dx = handle; int86 (0x67, &inregs, &outregs); if (outregs.h.ah != 0) { printf ("Error mapping pages %xH\n", outregs.h.ah); // Release the handle inregs.h.ah = 0x45; inregs.x.dx = handle; int86 (0x67, &inregs, &outregs); exit(0); } } // Fill the first four pages data = (char far *) MK_FP(page_frame_address, 0); for (index = 0; index < 16384; index++) data[index] = 'A'; for (index = 16384; index < 32768; index++) data[index] = 'B'; for (index = 32768; index < 49152; index++) data[index] = 'C'; for (index = 49152; index != 0; index++) data[index] = 'D'; // Map logical page 4 into physical page 1 inregs.h.ah = 0x44; inregs.h.al = 1; // Physical page inregs.x.bx = 4; // Logical page inregs.x.dx = handle; int86 (0x67, &inregs, &outregs); if (outregs.h.ah != 0) { printf ("Error mapping page %xH\n", outregs.h.ah); // Release the handle inregs.h.ah = 0x45; inregs.x.dx = handle; int86 (0x67, &inregs, &outregs); exit(0); } // Fill page 4 which resides in page 1 for (index = 16384; index < 32768; index++) data[index] = 'E'; // Display the first 20 bytes of each page printf ("Physical Page Zero\n"); for (index = 0; index < 20; index++) printf ("%c ", data[index]); printf ("\nPhysical Page One\n"); for (index = 16384; index < 16404; index++) printf ("%c ", data[index]); printf ("\nPhysical Page Two\n"); for (index = 32768; index < 32788; index++) printf ("%c ", data[index]); printf ("\nPhysical Page Three\n"); for (index = 49152; index < 49172; index++) printf ("%c ", data[index]); // Map logical page 1 into physical page 3 inregs.h.ah = 0x44; inregs.h.al = 3; // Physical page inregs.x.bx = 1; // Logical page inregs.x.dx = handle; int86 (0x67, &inregs, &outregs); if (outregs.h.ah != 0) { printf ("Error mapping page %xH\n", outregs.h.ah); // Release the handle inregs.h.ah = 0x45; inregs.x.dx = handle; int86 (0x67, &inregs, &outregs); exit(0); } printf ("\nMapping logical page 1 to physical page 3"); printf ("\nPhysical Page Three\n"); for (index = 49152; index < 49162; index++) printf ("%c ", data[index]); } else printf ("Error getting base address %xH\n", outregs.h.ah); // Release the handle inregs.h.ah = 0x45; inregs.x.dx = handle; int86 (0x67, &inregs, &outregs); } else printf ("Error allocating 5 pages %xH\n", outregs.h.ah); } else printf ("EMM not functional\n"); } else printf ("EMS driver not present\n"); }